Efficient preparation of nitrogen-doped carbon dots from corncobs cellulose to complex with europium ion as ratiometric fluorescence probe for visual detection of tetracycline

Tetracyclines (TC) is one type of widely used antibiotics and its persistent residues in aquaculture or excessive intake have caused serious threats to the environment and human health. Therefore, it is urgent need and vital to fabricate simple, feasible and accurate methods to monitor TC. In this work, corncobs cellulose, one type of agricultural waste, was chosen as raw material to prepare fluorescence nitrogen-doped carbon dots (N-CDs) through the hydrothermal method. The corncobs cellulose was firstly treated in the HNO 3 /H 3 PO 4 /NaNO 2 oxidants in order to improve its water dispersibility and active groups amounts, which was effectively in enhancing quantum yields of N-CDs up to 41.69 %. The blue fluorescent light of N-CDs at 468 nm was quenched by the TC, whereas the red fluorescence of europium ion (Eu 3+ ) at 615 nm was sensitized via its coordination with TC. Based on this reverse response, a ratiometric fluorescence probe was established by integrating the N-CDs with Eu 3+ . The probe displayed outstanding sensitivity and selectivity in recognition of TC, whose limit of detection (LOD) value was 0.15 μM in a wide linear range of 0–60 μM. Furthermore, it could be observed the fluorescence color changes from blue to red through the naked eyes, and thus a smartphone-assisted assay was successfully set up by establishing the relationships between the fluorescence color variations and the TC concentrations using the color acquisition software on smartphone. The results in the manuscript were not only beneficial for opening ways for high-value utilization of agricultural waste, but also gave insights on developing on-site and portable methods for visual monitoring TC in real samples.